3.12 Gas piping
Note
Due to the precision of modern modulating boilers it is important to pay special attention to
gas pressure regulation.
Important: Check gas supply pressure to each boiler with a manometer or other high-
quality precision measuring device. Pressure should be monitored before firing the boiler,
during operation throughout the boiler's full modulation range, and after the call when the
regulator is in a "lock-up" condition.
Pay special attention to retrofit situations where existing regulators may have an over-sized
orifice and/or worn seats, causing pressure “creep” and high lock-up pressures.
A high quality regulator will maintain constant pressure above the boiler’s minimum
specification at all firing rates, and will not exceed the boiler’s maximum pressure rating
when locked-up with no load.
3.12.1 Gas pressure
The boilers require a minimum inlet gas supply pressure of 4.0" w.c. for natural gas or propane during
high fire operation. For either fuel, the inlet pressure shall be no greater than 14.0" w.c. Confirm this
pressure range is available with your local gas supplier.
The inlet gas connection to the boiler is ½" NPT (female).
Adequate gas supply piping must be installed with no smaller than ½" Schedule 40 (e.g., Iron Pipe
Size (IPS) and using a 1" w.c. pressure drop, in accordance with the following chart.
Maximum Gas Pipe Length (ft)
Model ½" IPS ¾" IPS 1" IPS 1¼ " IPS
VX 110 (natural gas) 30' 125' 400' 1,600
VX 110 (propane) 90' 350' 1000' 2,000
VX 150 (natural gas) 20' 80' 200' 900'
VX 150 (propane) 50' 200' 600' 2,000'
VX 199 (natural gas) 10' 40' 150' 900'
VX 199 (propane) 30' 125' 400' 1,400'
Table 9 Maximum Gas Pipe Length (ft)
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